The present invention relates to a circuit for operating a load, in particular an operating circuit for a low-pressure discharge lamp. It is primarily concerned with an operating circuit in which a rectified AC supply voltage is used to operate a half-bridge oscillator as frequency generator for lamp operation. Nevertheless, the invention is not restricted either to a lamp as load or to a half-bridge oscillator.
A significant criterion for practical application of such circuits is electromagnetic compatibility with regard to interference sent into the mains power supply and with regard to the harmonic content of the supply current drawn. A further development of such a circuit which is very effective in this respect consists in introducing at least one pump path between the load circuit side and the power supply side of the frequency generator structure. The pump paths generally contain capacitors as impedances--but not necessarily or necessarily exclusively. With regard to the prior art, reference is made to European Patents 0 244 644 B1, 0 253 224 B1 and 0 372 303 B1. Such pump paths serve to transfer charge within the circuit with the aim of improving the harmonic structure of the supply current consumption. With regard to electromagnetic compatibility, the IEC Standard 61000/3/2, Class C and Class D, in particular, is taken into consideration within the scope of this invention.
For the sake of clarity, the description is based on a relatively simple pump path structure which corresponds to FIG. 1 in EP 0 244 644 B1. The prior art cited additionally shows different pump path structures which are also more complicated. These and further conceivable variations as well are included in the subject-matter of the main claim.